revets00

Tried to find some answers on here without starting a new thread but no luck. How to you stop the heat from coming in on an 89 C4? I know they have some kind of electronic control valve that I don't even think you can buy anymore. I've put a manual ball valve in the heater line but it get's aggravating when you have to stop and raise the hood to turn the heater on.
How to you get to this valve and can it be fixed or replaced?

DanielRicany

You Should Be Able To Buy The Valve. It Is Always Circulating Until You Turn On The AC. When You Turn On The AC Vacuum Is Pulled From The Valve And Closes It.

Its Called A Heater Control Valve. That's What You Should Be Looking For When Searching For A Replacement.

65Z01

Sounsd like C68 system, if so have you verified the Air Mix valve actuator is moving the blend door properly?

vetteoz

'89 doesn't have the shut off valve; coolant flows through the core full time ;
as noted above only the blend door position controls the temp

revets00

I looked under there a while back and the doors seemed to be opening and closing. Just seems there is just too much heat coming in with the a/c off. Seems if the heat is off there should be no heat. I had a 77 vette back in the day and I put a manual valve on it to. These cars will burn you up in the summer driving slow in town. I tried checking on that last year and I was thinking there was some kind of control valve and it has been discontinued. I may be wrong.

Cliff Harris

The heater control valve on older cars is controlled by the HVAC programmer by a vacuum line. The newer HVAC programmers are missing the vacuum solenoid for the heater control valve so there is no way to retrofit one. I doubt that the signal is there from the HVAC control head to the HVAC programmer to close the heater control valve, so that's another reason it can't be retrofitted.

My car does have the heater control valve and it only closes if you have the HVAC in the AUTO mode.

vetteoz

As noted the heater core has hot coolant flow all the time.
The only thing that prevents heat into air stream is the door fully closing , possibly the foam seals are gone ?

Pull the BCM out and look in the hole to see if you have full blend door travel when the controls operated

gerardvg

I agree with the earlier post the heater box seals have had it, the heat from the engine bay can enter the cabin and bring heat from the heater.
Check you heater if the vacuum heater valve works, are the vacuum hoses good.

I also have two ball valves to turn off the coolant flow to and from the heater.
Even with the vacuum operated heater water valve working there is so much heat in the heater box. It would have been better design to have the heater box with all tje heat in the engine bay and a/c evaporator in the cabin.
May be time to pull the heater box and replace the old seals also check the damper seals correctly.

They would not have sold the car with constant heat entering the cabin with heater turned off.
Perhaps someone who got their c4 new can let us know how the cabin was in summer?
Cheers

vetteoz

I was talking about the foam seals inside the ducting that the blend door seals to stop airflow through the heater core.
In the unit out of my '89 they were just powder